On Wed, Dec 20, 2023 at 2:14 PM Marco Moock <m...@dorfdsl.de> wrote: > > Am 20.12.2023 um 14:04:41 Uhr schrieb Pocket: > > > [...] > > And could that be the reason to multiple sessions were opened from > > debian list servers? > > No, the reason is that SMTP doesn't specify that only a special > amount of connections can be established, but your provider enforces > that and give back a hard fail (5xx error).
In the old days (up until about the mid 2000s or early 2010s, the Hosts RFC set the limit of concurrent connections to a host to 2. The last time I checked, that limitation was removed from the RFCs. Probably to pander to Browsers so they [the browsers] could have multiple requests in-flight. (The IETF appears to be captured by the CA/BF). It would not surprise me if the "2 concurrent connection" artifact was still lurking around somewhere, like in Majordomo. Jeff
